Alloy powder for forming hard phase and ferriferous mixed powder using the same, and manufacturing method for wear resistant sintered alloy and wear resistant sintered alloy

ABSTRACT

Alloy powder for forming a hard phase for a valve seat material having excellent high temperature wear resistance. The overall composition is consisted of Mo: 48 to 60 mass %, Cr: 3 to 12 mass % and Si: 1 to 5 mass %, and the balance of Co and inevitable impurities.

This is a Division of application Ser. No. 10/990,548 filed Nov. 18,2004. The entire disclosure of the prior application is herebyincorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wear resistant sintered alloy used invalve seat materials for automotive engines and to a manufacturingmethod therefor, and more particularly, relates to a developingtechnology of sintered alloy which may be advantageously used in valveseats in heavy duty engine such as CNG engine or diesel engine.

2. Description of the Related Art

Recently, engines for automobile are sever in operating condition towardhigh performance, and valve seats are required to withstand in moreextreme environmental conditions than ever. For example, in LPG engineswidely used in taxicabs, contacting surfaces of valves and valve seatsare used in a dry condition, and they become worn more quickly than ingasoline engines. In environments having heavy sludge deposits such asin high leaded gasoline engines with high lead content, the wear isincreased by the sludge when the surface pressure on the valve seat ishigh or when high temperature and high compression ratio is applied suchas in diesel engines. When used in such severe environments, a highstrength which does not cause a phenomenon of a plastic deformation isrequired for high wear resistance.

On the other hand, in order to adjust the valve position and valvedriving timing automatically, a dynamic valve mechanism having a lashadjuster has been developed, but the problem of engine life due to wearof valve seats is not solved sufficiently, and development of a valveseat material which is excellent in wear resistance has been demanded.More recently, aside from higher performance, development of economicaland inexpensive engines is equally important, and hence the sinteredalloy for valve seats must have high temperature wear resistance andhigh strength without requiring additional mechanisms such as a lashadjuster.

As such a sintered alloy for valve seats, Japanese Patent PublicationNo. S59-037343 (patent reference 1) (U.S. Pat. No. 4,422,875, U.S. Pat.No. 4,552,590) proposes to disperse Co—Mo—Si hard phase in a dappledmatrix of a Fe—Co alloy and a Fe—Cr alloy. Japanese Patent PublicationNo. H05-0955593 (patent reference 2) proposes to disperse Co—Mo—Si hardphase in a Fe—Co alloy matrix. Japanese Patent Publication No.H07-098985 (patent reference 3) (U.S. Pat. No. 4,919,719) proposes todisperse Co—Mo—Si hard phase in a matrix adding Ni to a Fe—Co alloy.Japanese Laid-open Patent No. H02-163351(patent reference 4) proposes anFe matrix alloy dispersing Co—Mo—Si hard phase.

Hard phase in the alloys disposed in these patent references 1 to 4 havea Mo content of 40 mass % or less, but sintered alloys containing thesehard phase have considerable high temperature wear resistance and highstrength. However, sintered alloys having wear resistance and highstrength in high temperature are desired. For example, an improvedinvention discloses alloy powder for forming wear resistant hard phaseconsisted of Si: 1.0 to 12 mass %, Mo: 20 to 50 mass %, Mn: 0.5 to 5.0mass %, and balance of at least one of Fe, Ni, and Co, and inevitableimpurities (see Japanese Laid-open Patent No. 2002-356704, patentreference 5).

Thus, according to the demand of the times, various sintered materialswith excellent wear resistance which may be favorably used as valve seatmaterials have been proposed. However, in recent CNG engines, heavy dutydiesel engines for high output, the load on the valve seat material ismuch higher due to metal contact, and there is a keen desire to developmaterials having high wear resistance in all severe environments.

SUMMARY OF THE INVENTION

The invention provides a wear resistant sintered member for a valve seatmaterial exhibiting an excellent wear resistance at high temperature inenvironments of heavy duty engine such as in CNG engines, dieselengines, or the like, and a manufacturing method therefor.

The present inventors have analyzed the wear state in metal contactenvironments on the basis of the prior technical background, anddiscovered that the wear in environments occured metal contact is causedby plastic flow and adhesion starting from the matrix portion expectedhard particles. As a countermeasure, by increasing the Mo content andgrowing Mo silicide material, it has been found that start points ofwear can be decreased. Moreover, by increasing the Mo content andintegrally precipitated Mo silicide, it has also been found that thepinning effect of hard particles can be increased. On the basis of thesefindings, the present inventors have concluded that the wear resistancecan be enhanced substantially because occurrence of plastic flow andadhesion can be minimized.

More specifically, as the hard phase, it is a feature of the inventionto select Co and eliminate Mn as the balance of the matrix disclosed inpatent reference 5, thereby increasing the Mo content without increasingthe hardness of the powder, and growing the precipitating Mo silicideand integrally precipitating at the same time. In this hard phase, it isalso important to optimize the Si content by limiting to an extent forproducing necessary Mo silicide so as to decrease the hardness of thepowder and increase the Mo amount. The invention was completed on thebasis of such findings.

The invention is intended to realize such countermeasures, and toprovide an alloy powder for forming a hard phase, the alloy consistingof Mo: 48 to 60 mass %, Cr: 3 to 12 mass %, and Si: 1 to 5 mass %, andthe balance of Co and inevitable impurities.

The invention provides a ferriferous mixed powder for wear resistantsintered alloy in which 5 to 40 mass % of the alloy powder for forminghard phase described above is added to the iron based powder mixture forforming matrix.

A manufacturing method for wear resistant sintered member of theinvention includes preparing the ferriferous mixed powder for formingthe wear resistant sintered alloy described above, compacting into aspecified shape, and sintering the compacted powder at 1000 to 1200° C.in a non-oxidizing atmosphere. The wear resistant sintered member of theinvention thus manufactured includes 5 to 40 mass % of the Co base hardphase dispersed in the iron base matrix. The Co base hard phase composesof the precipitated material mainly composed of Mo silicide integrallyprecipitated in the Co alloy matrix. And the Co base hard phase isconsisted of Mo: 48 to 60 mass %, Cr: 3 to 12 mass %, and Si: 1 to 5mass %, and the balance of Co and inevitable impurities.

An aspect of wear resistant sintered alloy of the invention isconsisting of Mo: 5.26 to 28.47 mass %, Co: 1.15 to 19.2 mass %, Cr:0.25 to 6.6 mass %, Si: 0.05 to 2.0 mass %, V: 0.03 to 0.9 mass %, W:0.2 to 2.4 mass %, and C: 0.43 to 1.56 mass %, and the balance of Fe andinevitable impurities. Further, an aspect of wear resistant sinteredalloy of the invention has a structure of 5 to 40 mass % of Co base hardphase and 5 to 30 mass % of Fe base hard phase are dispersed in a matrixof a bainite phase or a mixed phase of bainaite and martensite. Said Cobase hard phase has a structure in which the precipitation of mainly Mosilicide is integrally precipitating in Co base alloy matrix of the Cobase hard phase. Said Fe base hard phase has a structure in whichgranular Cr carbide, Mo carbide, V carbide and W carbide areprecipitated and dispersed in the Fe base hard phase.

Another aspect of the wear resistant sintered alloy of the invention isconsisting Mo: 4.87 to 28.47 mass %, Co: 1.15 to 19.2 mass %, Cr: 0.25to 6.6 mass %, Si: 0.05 to 2.0 mass %, V: 0.03 to 0.9 mass %, W: 0.2 to2.4 mass %, C: 0.43 to 1.56 mass %, and Ni: 13 mass % or less, and thebalance of Fe and inevitable impurities. Further, another aspect of thewear resistant sintered alloy of the invention has a structure of 5 to40 mass % of 5 to 40 mass % of Co base hard phase and 5 to 30 mass % ofFe base hard phase are dispersed in matrix of the mix phase of bainite,martensite and austenite. Said Co base hard phase has a structure inwhich the precipitation of mainly Mo silicide is integrallyprecipitating in Co base alloy matrix of Co base hard phase. Said Febase hard phase has a structure in which granular Cr carbide, Mocarbide, V carbide, and W carbide is precipitated and dispersed in Febase hard phase.

According to the invention, by increasing the dispersion amount of hardparticles of hard phase more than in the prior art, start points of wearcan be decreased, and also by integrally precipitating the hardparticles, the pinning effect of hard phase can be increased, andoccurrence of plastic flow and adhesion can be minimized. Therefore, thewear resistance of hard phase can be further enhanced, and the sinteredalloy exhibiting an excellent high temperature wear resistance in highload engine environments can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a metallographic structure of wearresistant sintered member of the invention;

FIG. 2 is a schematic diagram of a metallographic structure of wearresistant sintered member in a prior art;

FIG. 3 is a schematic diagram of a metallographic structure of firstwear resistant sintered alloy of the invention;

FIG. 4 is a schematic diagram of a metallographic structure of secondwear resistant sintered alloy of the invention;

FIG. 5 is a graph of the relationship of wear and Mo amount in an alloypowder for forming a hard phase;

FIG. 6 is a graph of the relationship of wear and Cr amount in an alloypowder for forming a hard phase;

FIG. 7 is a graph of the relationship of wear and Si amount in an alloypowder for forming a hard phase;

FIG. 8 is a graph of the relationship of wear and content of alloypowder for forming a hard phase;

FIG. 9 is a graph of the relationship of wear and sintering temperature;

FIG. 10 is a graph of the relationship of wear and hard phase;

FIG. 11 is a graph of the relationship of wear and Mo amount in alloypowder B;

FIG. 12 is a graph of the relationship of wear and Si amount in alloypowder B;

FIG. 13 is a graph of the relationship of wear and Cr amount in alloypowder B;

FIG. 14 is a graph of the relationship of wear and content alloy powderB;

FIG. 15 is a graph of the relationship of wear and Mo amount in alloypowder A;

FIG. 16 is a graph of the relationship of wear and Mo amount in alloypowder C;

FIG. 17 is a graph of the relationship of wear and amount of alloyelements (V, W, Cr) in alloy powder C;

FIG. 18 is a graph of the relationship of wear and C amount in alloypowder C;

FIG. 19 is a graph of the relationship of wear and content of alloypowder C;

FIG. 20 is a graph of the relationship of wear and content of Ni powder;

FIG. 21 is a graph of the relationship of wear and content of graphitepowder; and

FIG. 22 is a graph of the relationship of wear and sinteringtemperature.

PREFERRED EMBODIMENTS OF THE INVENTION

Referring now to the drawings, the actions of alloy powder for forminghard phase and ferriferous mixed powder using the same, andmanufacturing method for wear resistant sintered member and wearresistant sintered member of the invention are described below togetherwith reasons for setting the numerical values.

(1) Alloy Powder for Forming Hard Phase

The alloy powder for forming the hard phase of the invention uses Co asa base material, which mainly diffuses in the Fe matrix when sinteringto strengthen the Fe matrix and contribute to enhancement of fixation ofhard particles, and is also effective in enhancing the heat resistanceof the hard phase and its periphery. A part of Co forms Mo—Co silicidetogether with Mo and Si, and is also effective in enhancing the wearresistance. The reasons for limiting the chemical composition of alloypowder for forming the hard phase are explained below.

Mo: Mo is mainly bonded with Si, and forms Mo silicide which is superiorin wear resistance and lubricity, thereby contributing to enhancement ofwear resistance of a sintered alloy. A part of Mo incorporates Co andforms hard particles of Mo silicide. If the Mo content is less than 48mass %, the Mo silicide is not integrated during precipitation, andgranular Mo silicide disperses in Co base hard phase as in the priorart, and the wear resistance remains at the conventional level. Incontract, if the Mo content exceeds 60 mass %, the effect of increasedMo becomes larger than the effect of eliminated Mn and decreased Sidescribed below, and the hardness of the powder becomes higher, and thecompactability in forming is decreased. And, the formed hard phasebecomes brittle, and the hard phase may be partly broken by impact, andthe broken particles act as abrasive. So the wear resistance may berather reduced by these reasons. Hence, the Mo content is specified tobe within 48 to 60 mass %.

Cr: Cr contributes to reinforcement of the Co matrix of the hard phase.It further diffuses into the Fe matrix and contributes to enhancement ofwear resistance of the Fe matrix. If the Cr content is less than 3 mass%, such effects are not expected. If the Cr content exceeds 12 mass %,the amount of powder oxygen increases, and an oxide film is formed onthe powder surface which impedes progress of sintering, and the powderis hardened by an oxide film, and compactability is reduced. As aresult, the strength of the sintered alloy is reduced and wearresistance decreases, and hence the upper limit of Cr content is 12 mass%. Thus, the Cr content is specified to be within 3 to 12 mass %.

Si: Si mainly reacts with Mo, and forms Mo silicide which is superior inwear resistance and lubricity, and thereby contributes to enhancement ofwear resistance of the sintered alloy. A certain diffusion of Si intothe matrix is effective for fixation of the hard phase into the matrix.If the Si content is less than 1 mass %, sufficient Mo silicide is notformed and sufficient improving effect of wear resistance is notobtained. If the Si content is excessive, instead of reacting with Mo,large amounts of Si diffuses into the matrix. Si hardens the Fe matrixand makes it brittle. Excessive diffusion of Si is not favorable becausethe wear resistance of Fe matrix is reduced and atackability isincreased. By decreasing the amount of Si not reacting with Mo, anappropriate Mo amount can be given without increasing the hardness ofthe powder. Hence, the upper limit of Si content is 5 mass % where Sidiffusing into the matrix without reacting with the Mo amount begins toincrease. Therefore, the Si content is specified toe be within 1 to 5mass %.

(2) Ferriferous Mixed Powder

The ferriferous mixed powder of the invention is composed of iron basealloy powder for forming iron alloy matrix, mixed with 5 to 40 mass % ofthe alloy powder for forming the hard phase described above. The higherthe content of the alloy powder for forming hard phase, the better thewear resistance. However, if the addition is less than 5 mass % of theoverall ferriferous mixed powder, the improvement in wear resistance isnot sufficient. If the addition is more than 40 mass %, thecompactability of mixed powder is reduced, and density and strengthafter sintering are reduced, and the wear resistance decreases. Hence,the addition of alloy powder for forming a hard phase is specified to bewithin 5 to 40 mass % of the overall ferriferous mixed powder. The ironbase alloy powder can be selected from at least one of alloy powder, mixpowder of iron powder and other elemental powder and mix powder of alloypowder.

(3) Manufacturing Method for Wear Resistant Sintered Member and WearResistant Sintered Member

The manufacturing method for a wear resistant sintered member of theinvention includes preparing alloy powder for forming a hard phaseconsisted of Mo: 48 to 60 mass %, Cr: 3 to 12 mass %, Si: 1 to 5 mass %,and balance: Co and inevitable impurities, adding 5 to 40 mass % of thealloy powder to a iron base alloy powder for forming an iron alloymatrix, thereby preparing a ferriferous mixed powder, compacting theferriferous mixed powder into a specified shape, and sintering thecompacted powder at 1000 to 1200° C. in a non-oxidizing atmosphere.

The reason for limiting the sintering temperature in the manufacturingmethod for the wear resistant sintered member is explained. Thecomposition of iron base powder for forming the iron alloy matrix is notparticularly specified, and any powder for forming a Fe alloy matrix inpatent references 1 to 3 and others may be used. The iron base powderfor forming the iron alloy matrix may be either an alloy powder or amixed powder. That is, the wear resistance can be enhanced merely byreplacing the Co base hard phase used in the prior art with the Co basehard phase of the invention. However, if the sintering temperature isless than 1000° C., sintering is not sufficient, and satisfactory wearresistance is not obtained. If the sintering temperature exceeds 1200°C., the hard phase is melted and lost, and necessary components forintegrally precipitating the Mo silicide diffuse and flow out into thematrix, and the Mo silicide becomes precipitated material in granularform. Hence, the sintering temperature is specified to be within 1000 to1200° C.

This manufacturing method brings about a wear resistant sintered alloyin which 5 to 40 mass % of Co base hard phase, in which a precipitatedmaterial mainly made of Mo silicide is integrally precipitated, isdispersed in a ferriferous alloy matrix of sintered member, the Co basehard phase comprising Mo: 48 to 60 mass %, Cr: 3 to 12 mass %, Si: 1 to5 mass %, and balance of Co and inevitable impurities. In this wearresistant sintered alloy, as shown in FIG. 1, the hard phase composed ofhard particles and Co base matrix. The hard particles mainly made of Mosilicide are integrally precipitated in the Co base matrix of Co alloyphase (white phase), and the Co base matrix formed in the inside and atthe periphery of the hard particles. This hard phase is dispersed in thematrix of sintered member and bonded firmly to the matrix of sinteredmember by diffusing Co of the Co base matrix. This hard phase enhancesthe wear resistance by the Mo silicide which is hard and low affinityfor valve as a contacting member. This hard particles which mainly madeof Mo silicide are integrally precipitated, and effectively prevent thewear by pinning effect of matrix which is occurred by plastic flow oradhesion of the matrix even in the metal contact inducing environment.

By contrast, FIG. 2 shows a schematic diagram of conventional wearresistant sintered member. In this wear resistant sintered member, ahard phase surrounded by a diffuse phase (white phase) diffusing Coaround the core of granular hard particles mainly made of Mo silicide isdiffused in the matrix of sintered alloy. This hard phase is hard, butis not formed by integral precipitation of hard particles of Mosilicide, the matrix pinning effect is small, and wear due to plasticflow or adhesion cannot be sufficiently prevented.

These are the actions of a wear resistant sintered member of theinvention, and the actions of a wear resistant sintered alloy of theinvention are described below while referring to the accompanyingdrawings, together with the reasons of setting the numerical values.

(1) Matrix

FIG. 3 is a schematic diagram showing a metallographic structure of thefirst wear resistant sintered alloy. As shown in the diagram, the matrixstructure of this sintered alloy is mainly composed of bainite.Martensite has a hard and strong structure and is effective forenhancing the wear resistance, but because of its hardness, it promoteswear of the valve as a contacting member. Matrix structure is mainlycomposed of Bainite which is not as hard as martensite and is hard andstrong next to martensite. Therefore, Bainaite can decrease the damageto the contacting member while preventing plastic flow of the matrix.Bainite may be used alone, or martensite may be dispersed in the matrixstructure of bainite in order to further enhance the wear resistance.The wear resistance is further improved by dispersing the hard phase ofthe invention in the matrix of bainite single phase or bainite andmartensite mixed phase having excellent wear resistance.

To obtain such a matrix, as the matrix component, an iron base alloycontaining Mo by 3 to 7 mass % is suitable, and it is provided in a formof iron base alloy powder (alloy powder A). Mo is solved by solidsolution in an iron matrix, and acts to expand the bainite region, andcontributes to bainite formation of a matrix structure at ordinarycooling rates after sintering. However, if the amount of Mo is less than3 mass % of iron base alloy powder, its action becomes poor, or if itexceeds 7 mass %, the alloy powder becomes harder and compactability isworsened.

On the other hand, FIG. 4 is a schematic diagram showing ametallographic structure of the second wear resistant sintered alloy. Asshown in the diagram, the matrix of this wear resistant sintered alloyis a mixed structure of martensite with high strength and austenite withhigh toughness dispersed in bainite. In this structure, the toughaustenite lessens the atackability of martensite, and the soft andplastically flowing austenite is reinforced by the martensite of highstrength and having matrix plastic flow preventive effect, and they havemutually complementary effects, and a further improving effect of wearresistance is obtained.

Such a matrix structure can be obtained by adding Ni powder to the ironbase alloy powder containing Mo (alloy powder A). That is, in thesintering process, Ni diffusing into the iron matrix from Ni powderpresents a concentration profile of high Ni concentration in theoriginal Ni powder portion, and decreasing concentration as moving awayfrom the original Ni powder portion. Ni has an action improvinghardenability, in the Ni diffusing region, it is transformed into amartensite structure in the cooling process after sintering, the high Niconcentration portion remains as austenite even at ordinary temperature,thereby forming this matrix structure. However, if the added amount ofNi powder is more than 13 mass %, the remaining austenite amount isexcessive, and the Ni diffusion amount is too large, and the bainitestructure does not remain, and hence the upper limit must be set at 13mass %.

(2) Hard Phase

In either one of the first and second wear resistant sintered alloys ofthe invention, as shown in FIG. 3 and FIG. 4, hard phase (first hardphase) is dispersed in the matrix of sintered alloy. The hard phase(first hard phase) is composed of hard particles which mainly made ofintegrally precipitated Mo silicide and Co alloy phase (white phase)which is formed in the inside and at the periphery of the integrallyprecipitated Mo silicide. The hard phase is bonded firmly to the matrixof sintered alloy by diffusing Co of the Co alloy phase. This hard phaseenhances the wear resistance by the Mo silicide which is hard and low inaffinity with the contacting member of a valve. This hard phaseeffectively prevent the wear by matrix pinning effect which is occurredplastic flow or adhesion of the matrix even in a metal contact inducingenvironment, since hard particles mainly made of Mo silicide areintegrally precipitated.

In either one of the first and second wear resistant sintered alloys ofthe invention, an Fe base hard phase (second hard phase) is diffuseddispersed in the matrix of sintered alloy. In the Fe base hard phase(second hard phase), granular Cr carbide, Mo carbide, V carbide, and Wcarbide are mainly precipitated. Fe base alloy matrix of Fe base hardphase is formed in the periphery of these carbides. This hard phase is acomposition known as Molybdenum high speed steel.

Among such hard phases, the Co base hard phase provides an extremelysuperior wear resistance when dispersed in the matrix at 5 to 40 mass %.If it is less than 5 mass %, the improving effect of wear resistance isnot sufficient, or if it exceeds 40 mass %, the compactability of themixed powder is reduced, and the atackability becomes higher, and thewear amount undesirably increases. Similarly, the Fe base hard phaseprovides an extremely superior wear resistance when dispersed in thematrix at 5 to 30 mass %. If it is less than 5 mass %, the improvingeffect of wear resistance is not sufficient, or if it exceeds 30 mass %,the compactability of mixed powder is reduced, and the atackabilitybecomes higher, and the wear amount undesirably increases.

The reasons for limiting the chemical composition are explained below.

Mo: Mo is solved by a solid solution in the matrix to strengthen thematrix, and expands the bainite region of the matrix, and functions totransform the matrix into bainite by ordinary cooling after sintering,without requiring any particular isothermal treatment. By suchfunctions, Mo contributes to enhancement of strength and wear resistanceof the matrix of sintered alloy. In the first hard phase, Mo forms ahard silicide together with Si, and partly reacts with Co to form Mo—Cosilicide, and these Mo silicides are integrally precipitated to formcores of hard phase to prevent plastic flow and adhesion of matrix,thereby contributing to enhancement of wear resistance. In the secondhard phase, Mo forms granular Mo carbides to contribute to enhancementof wear resistance.

If the content of Mo is less than 3 mass % as the amount provided as asolid solution in the matrix, bainite formation of matrix is notsufficient, and the strength and wear resistance are insufficient. Ifthe amount in the first hard phase is less than 48 mass %, the Mosilicide is not integrally precipitated, but is precipitated as Mosilicide portion, and the wear resistance is reduced. If the amount inthe second hard phase is less than 4 mass %, the forming amount of Mocarbide becomes insufficient, and the wear resistance is reduced. Thelower limit of the amount of Mo in the overall composition is 5.26 mass% in the first wear resistant sintered alloy, and 4.87 mass % in thesecond wear resistant sintered alloy.

On the other hand, if the amount given as a solid solution in the matrixis more than 7 mass %, and the amount in the first hard phase is morethan 60 mass %, and the amount in the second hard phase is more than 8mass %, the material powder as the supply source is too hard and thecompactability is reduced, and the density of forming is reduced, andthe density is not increased after sintering, and the strength and wearresistance are reduced. In the overall composition, the upper limit ofthe Mo amount is 28.47 mass %.

Therefore, the Mo content is specified to be within 5.26 to 28.47 mass %in the first wear resistant sintered alloy, and 4.87 to 28.47 mass % inthe second wear resistant sintered alloy.

Co: Co in the first hard phase diffuses in the matrix to reinforce bythe solid solution of the matrix of sintered alloy, and functions tobond the hard phase firmly to the matrix. The Co diffusing into thematrix strengthens the matrix, and also acts to improve the heatresistance of the matrix of sintered alloy and the hard phase. Inaddition, some of the Co forms Mo—Co silicide together with Mo and Si,and forms the core of the hard phase to prevent plastic flow andadhesion of the matrix, thereby contributing to enhancement of wearresistance. If the content of Co exceeds 19.2 mass %, the powder of thesupply source becomes hard, and the compactability is decreased. Thelower limit is 1.15 mass %. If it is lower than this lower limit, theeffect is not sufficient. Hence, the content of Co is specified to bewithin 1.15 to 19.2 mass %.

Cr: Cr in the first hard phase is solved by a solid solution in the Comatrix of the first hard phase and acts to strengthen. Cr in the secondhard phase forms carbide and contributes to enhancement of wearresistance of the matrix. Further, Cr diffusing into the matrix from thefirst and second hard phases bonds the hard phase firmly to the matrixof sintered alloy, and is solved by a solid solution in the matrix tostrengthen the matrix further, and functions to enhance thehardenability further. The effect is not sufficient if the content of Cris less than 3 mass % in the first hard phase, or less than 2 mass % inthe second hard phase. The lower limit of the Co amount in the overallcomposition is 0.25 mass %. On the other hand, if the amount in thefirst hard phase is more than 12 mass % and the amount in the secondhard phase is more than 6 mass %, the powder of the supply sourcebecomes hard, and the compactability is decreased. Hence, the upperlimit of Cr amount in the overall composition is 6.6 mass %. The contentof Cr is specified within 0.25 to 6.6 mass %.

Si: Si is compounded with Mo and Co in the first hard phase as mentionedabove, and forms hard Mo silicide and Mo—Co silicide, and contributes toenhancement of wear resistance. If the content of Si is less than 0.05mass %, sufficient amount of silicide is not precipitated, or if itexceeds 2.0 mass %, the powder of the supply source becomes hard, andthe compactability is decreased, and the sintering property is worsened.Hence, the content of Si is specified to be within 0.05 to 2.0 mass %.

V: V forms a fine V carbide in the second hard phase to contribute toenhancement of wear resistance, and partly diffuses into the matrix tostrengthen by the solid solution. If the content of V is less than 0.03mass %, the effect is insufficient. If it exceeds 0.9 mass %, the powderof the supply source becomes hard and the compactability is decreased.Hence, the content of V is specified within 0.03 to 0.9 mass %.

W: Like V, W also forms carbide in the second hard phase to contributeto enhancement of wear resistance. If the content of W is less than 0.2mass %, the effect is insufficient. If it exceeds 2.4 mass %, the powderof the supply source becomes hard and the compactability is decreased.Hence, the content of W is specified toe be within 0.2 to 2.4 mass %.

C: C functions to strengthen the matrix of the sintered alloy, andcontributes to formation of bainite, martensite and austenite in thematrix structure, thereby enhancing the wear resistance. In the secondhard phase, as mentioned above, it forms granular carbides and granularmixed carbides of Mo, Cr, V, and W, and contributes to enhancement ofwear resistance. If the content of C is less than 0.43 mass %, ferritehaving low wear resistance and low strength remains in the matrixstructure, and improvement of wear resistance is not sufficient. If thecontent of C exceeds 1.56 mass %, cementite begins to precipitate in thegrain boundary, and the strength is reduced. Hence, the content of C isspecified to be within 0.43 to 1.56 mass %.

Ni: By addition of a small amount thereof, Ni contributes to reinforcethe matrix by the solid solution, and improves the hardenability of thematrix structure, and promotes formation of martensite at cooling rateafter sintering to contribute to enhancement of wear resistance. A highconcentration portion of Ni remains as austenite. Since the austenitestructure is soft and tough, austenite effectively suppresses attack onthe contacting member. In the second sintered alloy of the invention, itis required to form bainite or a mixed structure of martensite andaustenite in addition to bainite, and a certain quantity of Ni isneeded. However, excessive Ni content may cause excessive formation oftough and soft austenite, and plastic flow or adhesion of the matrix maybe easily to occur, or bainite may not remain in the matrix structure,and the wear resistance may be reduced. Hence, the upper limit of Nicontent is 13 mass %. In the wear resistant sintered alloy of theinvention, Ni is contained in the second wear resistant sintered alloyonly.

Herein, the first or second wear resistant sintered alloy has ametallographic structure in which 0.3 to 2.0 mass % of at least one typeof machinability improving particles selected from the group consistingof lead, molybdenum disulfide, manganese sulfide, boron nitride,magnesium metasilicate mineral, and calcium fluoride is preferablydispersed. These are machinability improving components, and bydispersing in the matrix, they become starting points of breaking duringmachining, so that the machinability of the sintered alloy can beimproved. If the content of such machinability improving components isless than 0.3 mass %, the effect is insufficient, or if it is containedat more than 2.0 mass %, the strength of the sintered alloy is reduced.Hence, the content is specified to be within 0.3 to 2.0 mass %.

In the wear resistant sintered alloy of the invention, preferably, atleast one type selected from the group consisting of lead, lead alloy,copper, copper alloy and acrylic resin should be infiltrated orimpregnated in the pores. They are also machinability improvingcomponents. In particular, when a porous sintered alloy is machined,machining condition is intermittent, but when pores are filled with leador copper, cutting condition is continuous, and impact on the tip of thetool is reduced. The lead also functions as a solid lubricant, and thecopper or copper alloy is high in heat conductivity and preventsgathering of heat, and lessens heat damage of the tool tip, and theacrylic resin acts as start points of cutting tip breaking.

The manufacturing method for first and second wear resistant sinteredalloys of the invention is described below.

The manufacturing method for the first wear resistant sintered alloyincludes preparing a mixed powder of alloy powder A for forming a matrixconsisted of Mo: 3 to 7 mass % and balance: Fe and inevitableimpurities, added 5 to 40 mass % of alloy powder B for forming Co basehard phase consisted of Mo: 48 to 60 mass %, Cr: 3 to 12 mass %, Si: 1to 5 mass %, and balance: Co and inevitable impurities, 5 to 30 mass %of alloy powder C for forming Fe base hard phase consisted of Mo: 4 to 8mass %, V: 0.5 to 3 mass %, W: 4 to 8 mass %, Cr: 2 to 6 mass %, C: 0.6to 1.2 mass %, and balance: Fe and inevitable impurities, and 0.3 to 1.2mass % of graphite powder, compacting the mixed powder into a specifiedshape, and sintering the compacted powder at 1000 to 1200° C. in anon-oxidizing atmosphere.

The manufacturing method for the second wear resistant sintered alloyincludes preparing a mixed powder of alloy powder A for forming a matrixconsisted of Mo: 3 to 7 mass % and balance: Fe and inevitableimpurities, added 5 to 40 mass % of alloy powder B for forming Co basehard phase consisted of Mo: 48 to 60 mass %, Cr: 3 to 12 mass %, Si: 1to 5 mass %, and balance: Co and inevitable impurities, 5 to 30 mass %of alloy powder C for forming Fe base hard phase consisted of Mo: 4 to 8mass %, V: 0.5 to 3 mass %, W: 4 to 8 mass %, Cr: 2 to 6 mass %, C: 0.6to 1.2 mass %, and balance: Fe and inevitable impurities, 13 mass % orless of Ni powder, and 0.3 to 1.2 mass % of graphite powder, compactingthe mixed powder into a specified shape, and sintering the compactedpowder at 1000 to 1200° C. in a non-oxidizing atmosphere.

The elements of these powder materials and the reasons for limiting thecontents of the elements are described below in the order of powder forforming the matrix and the mixed powder.

(1) Power for Forming Matrix

Alloy Powder A

Mo: Mo is an element which facilitates formation of a bainite structureat cooling rate in a furnace after sintering, and, forms Mo carbide tocontribute to enhancement of wear resistance. Mo is also effective inincreasing the resistance to tempersoftening of the matrix, and it iseffective to prevent plastic deformation during use in the case of asintered alloy for a valve seat repeated heating and cooling. If thecontent of Mo is less than 3 mass %, such effects are insufficient, andpearlite remains in the matrix structure, and the effect of enhancingthe wear resistance becomes poor. If the content of Mo exceeds 7 mass %,these effects becomes extremely and Mo carbide in hypereutectoid regionis easily to precipitate, and machinability is reduced and atackabilityis increased. The content of Mo is specified to be within 3 to 7 mass %.In order to enhance these actions of Mo uniformly on the entire matrix,Mo is preferred to be given in a form of Fe—Mo alloy powder.

(2) Powder for Mixing

In order to disperse the hard phase and provide wear resistance in thematrix formed of alloy powder A, alloy powder B made of Co base alloy,alloy powder C made of Fe base alloy, and graphite powder are preparedas powder for mixing. When manufacturing the second wear resistantsintered alloy, Ni powder is further prepared.

Alloy Powder B (for Forming Co Base Hard Phase)

Co: Co diffuses in a matrix to bond the hard phase firmly to the matrix.Diffusing in the matrix, Co strengthens the matrix of sintered alloy,and also acts to improve the heat resistance of the matrix of sinteredalloy and matrix of the hard phase. Part of Co forms, together with Moand Si, Mo—Co silicide, and this silicide becomes the core of the hardphase to contribute to enhancement of wear resistance, and also by thepinning effect, plastic flow or adhesion of matrix can be prevented.Hence, alloy powder B is composed of Co alloy powder. Reasons forlimiting the chemical composition contained in the alloy powder B andmixing ratio of alloy powder B are explained below.

Mo: Mo is mainly bonded with Si, and forms integrally Mo silicide whichis superior in wear resistance and lubricity, thereby contributing toenhancement of wear resistance of the sintered alloy. In part, Moincorporates also Co and forms hard particles of Mo—Co silicide. If theMo content in the alloy powder B is less than 48 mass %, the Mo silicideis not integrated and is granulated in precipitation, and the wearresistance remains at the conventional level. In contrast, if the Cocontent in alloy powder B exceeds 60 mass %, the effect of increment ofMo is promoted, and the hardness of the powder becomes higher, and thecompactability in forming is decreased. At the same time, the formedhard phase becomes brittle, and it may be partly broken by impact, andthe wear resistance may be somewhat reduced by the action of theabrasive. Hence, the Mo content in alloy powder B is specified to bewithin 48 to 60 mass %.

Cr: Cr contributes to reinforcement of the Co matrix of the hard phase.It further diffuses into the Fe matrix of sintered alloy, andcontributes to enhancement of wear resistance of the Fe matrix ofsintered alloy. If the Cr content in alloy powder B is less than 3 mass%, such effects becomes If the Cr content exceeds 12 mass %, the amountof powder oxygen increases, and an oxide film is formed on the powdersurface to impede progress of sintering, and the powder is hardened bythe oxide film, and compactability is reduced. As a result, the strengthof sintered alloy is reduced and wear resistance decreases, and hencethe upper limit of Cr content is 12 mass %. Thus, the Cr content in thealloy powder B is specified to be within 3 to 12 mass %.

Si: Si mainly reacts with Mo, and forms Mo silicide which is superior inwear resistance and lubricity, and thereby contributes to enhancement ofwear resistance of the sintered alloy. A certain diffusion of Si intothe matrix is effective for fixation of the hard phase into the matrix.If the Si content in the alloy powder B is less than 1 mass %,sufficient Mo silicide is not precipitated, and sufficient improvingeffect of wear resistance is not obtained. If the Si content isexcessive, instead of reacting with Mo, a large amount of Si diffusesinto the matrix of sintered alloy. Si hardens the Fe matrix and makes itbrittle at the same time. Excessive diffusion of Si is not desirablebecause the wear resistance of Fe matrix of sintered alloy is reducedand atackability is increased. By decreasing the amount of Si notreacting with Mo, an appropriate amount of Mo can be given withoutincreasing the hardness of the powder. Hence, the upper limit of Sicontent is 5 mass % where Si diffusing into the matrix without reactingwith Mo amount begins to increase. Therefore, the Si content isspecified to be within 1 to 5 mass %.

The addition amount of alloy powder B is explained. As mentioned above,the hard phase by alloy powder B is firmly bonded to the matrix, and theoriginal powder portion is integrated with hard particles mainly made ofMo silicide and also forming a precipitating structure of Co alloy phase(white phase) of high Co and Cr concentration in the inside and at theperiphery of hard particles, thereby forming a hard phase. The higherthe content of alloy powder B, the better the wear resistance. However,if the addition is less than 5 mass % of the overall mixed powder, thepinning effect of the matrix of sintered alloy is insufficient in themetal contact inducing environment, and plastic flow or adhesion ofmatrix of sintered alloy occurs, which promotes wear, and the improvingeffect of wear resistance becomes poor. In contrast, if the amountexceeds 40 mass %, the compactability of the mixed powder is low, andthe density and strength after sintering decrease, and the wearresistance also decreased. Hence, the amount of alloy powder B in theoverall mixed powder is specified to be within 5 to 40 mass %.

Alloy Powder C (for Forming Fe Base Hard Phase)

Fe: Herein, Fe is the matrix of a so-called Molybdenum high speed steel,and contributes to enhancement of wear resistance. Hence, alloy powder Cis composed of Fe base alloy. Reasons for limiting the chemicalcomposition contained in alloy powder C and mixing ratio of alloy powderC are explained below.

Mo: Mo forms carbide and contributes to enhancement of wear resistance.It further diffuses into the matrix of sintered alloy and functions toincrease fixation of the hard phase to the matrix. If the Mo content inalloy powder C is less than 4 mass %, the amount of precipitating Mocarbide is insufficient, and the wear resistance improving effectbecomes poor. In contrast, if the content exceeds 8 mass %, the amountof precipitating Mo carbide becomes excessive, and the atackability isincreased, and the machinability is extremely reduced. Hence, the Mocontent in alloy powder C is specified to be within 4 to 8 mass %.

V: V forms hard and fine V carbide particles, and contributes toenhancement of wear resistance. This effect is prominent when the Vcontent in alloy powder C is 0.5 mass % or more, but if it exceeds 3mass %, the amount of precipitating V carbide is excessive, and theatackability is increased, and the machinability is extremely reduced.Hence, the V content in alloy powder C is specified to be within 0.5 to3 mass %.

W: V forms hard W carbide particles and contributes to enhancement ofwear resistance. If the W content in alloy powder C is less than 4 mass%, the amount of precipitating W carbide is insufficient, and the wearresistance improving effect becomes poor. However, it exceeds 8 mass %,the amount of precipitating W carbide is excessive, the atackability isincreased, and the machinability is extremely reduced. Hence, the Wcontent in alloy powder C is specified to be within 4 to 8 mass %.

Cr: Cr forms a carbide and contributes to enhancement of wearresistance. It further diffuses into the matrix atackability toreinforce fixation of the hard phase to the matrix, and improves thehardenability of the matrix to transform the matrix structure intomartensite in the cooling process after sintering, thereby enhancing thewear resistance of the matrix. If the Cr content in alloy powder C isless than 2 mass %, the amount of precipitating Cr carbide isinsufficient, and the improving effect of wear resistance is notsufficient. If it exceeds 6 mass %, the amount of precipitating Crcarbide becomes too large, and the atackability is increased, and themachinability is extremely reduced. Hence, the Cr content in alloypowder C is specified to be within 2 to 6 mass %.

C: When these alloy components are given to the Fe alloy powder in theform of a solid solution, the powder becomes too hard, and thecompactability is extremely reduced. Accordingly, C is added to the Febase alloy powder, and part of the alloy components forming the solidsolution in the Fe alloy powder is caused to precipitate in the form ofa carbide. As a result, carbide is precipitated and disperses in the Febase alloy powder, but the alloy components solved by a solid solutionin the matrix portion of the Fe alloy powder are decreased. Hence, inthe overall Fe base alloy powder, the hardness of the powder is reduced,and the compactability is improved. If the content of C in the C alloypowder given to the Fe base alloy is less than 0.6 mass %, the amount ofprecipitating carbide becomes small, and the improvement ofcompactability is not sufficient. If it is provided at more than 1.2mass %, the amount of carbide precipitating in the Fe base alloy powderbecomes too large, and the compactability decreased. Hence, the contentof C in alloy powder C is specified to be within 0.6 to 1.2 mass %.

The amount of addition of alloy powder C is explained. When alloy powderC is dispersed in the matrix at 5 to 30 mass %, an extremely superiorwear resistance is exhibited. If the amount of alloy powder C in thetotal mass of mixed powder is less than 5 mass %, the improving effectof wear resistance is not sufficient, and it exceeds 30 mass %, thecompactability of mixed powder is reduced, the atackability is higher,and the amount of wear increases. Hence, the amount of alloy powder C inthe overall mass of mixed powder is specified to be within 5 to 30 mass%.

Ni Powder

Ni reinforces the matrix by a solid solution, and it is added to make iteasier to form martensite at ordinary cooling rate after sintering. WhenNi is given in a form of solid solution in Fe—Mo alloy powder, Ni isuniform, and bainite single-phase structure is easily obtained. If Ni isgiven as a single powder or is partly dispersed in Fe—Mo alloy powder,high Ni concentration parts are dispersed in the matrix. The portiondiffused Ni are transformed into martensite, and martensite is easily tobe dispersed in the bainite structure. If used as a single powder, theoriginal Ni powder portion is high in Ni concentration, and remains astough austenite, and functions to enhance the toughness of the matrix.However, if austenite disperses excessively, the wear resistance isreduced, and the Ni content should be controlled to within 13 mass % ofthe overall mass of the mixed powder. In the wear resistant sinteredalloy of the invention, Ni is contained only in the second wearresistant sintered alloy.

Graphite Powder

When C is added to alloy power A for forming matrix in the form of asolid solution, the alloy power becomes hard and the compactabilitydecreases, and therefore it is added in the form of graphite. When addedin the form of graphite, C strengthens the matrix of sintered alloy andenhances the wear resistance. Further, part of graphite powder formscarbide of Cr, Mo, V and W in alloy powder C and/or mixed carbide ofthem. If the amount of C is less than 0.3 mass %, ferrite which is lowin wear resistance and strength is remained in the matrix structure, andif it exceeds 1.2 mass %, cementite begins to precipitate in the grainboundary, and the strength is reduced. Hence, the addition of graphiteis specified to be within 0.3 to 1.2 mass % for the mass of alloy powderA for forming the matrix.

The first wear resistant sintered member of the invention manufacturedby using specified amounts of alloy powder A, alloy powder B, alloypowder C, and graphite powder. In the first wear resistant sinteredmember, overall composition is that Mo: 5.26 to 28.47 mass %, Co: 1.15to 19.2 mass %, Cr: 0.25 to 6.6 mass %, Si: 0.05 to 2.0 mass %, V: 0.03to 0.9 mass %, W: 0.2 to 2.4 mass %, and C: 0.43 to 1.56 mass %, and thebalance of Fe and inevitable impurities. Further, in the first wearresistant sintered member, 5 to 40 mass % of Co base hard phase and 5 to30 mass % of Fe base hard phase are dispersed in matrix structurecomposed of bainite phase or mixed phase of bainite and martensite. TheCo base hard phase includes the precipitated material mainly composed ofMo silicide integrally precipitated in the Co base hard phase. The Febase hard phase includes granular Cr carbide, Mo carbide, V carbide, andW carbide precipitated in the Fe base hard phase.

The second wear resistant sintered member of the invention manufacturedby using specified amounts of alloy powder A, alloy powder B, alloypowder C, Ni powder, and graphite powder. Further, in the second wearresistant sintered member, overall composition is that Mo: 4.87 to 28.47mass %, Co: 1.15 to 19.2 mass %, Cr: 0.25 to 6.6 mass %, Si: 0.05 to 2.0mass %, V: 0.03 to 0.9 mass %, W: 0.2 to 2.4 mass %, C: 0.43 to 1.56mass %, and Ni: 13 mass % or less, and the balance of Fe and inevitableimpurities. In the second wear resistant sintered member, 5 to 40 mass %of Co base hard phase and 5 to 30 mass % of Fe base hard phase aredispersed in matrix structure composed of bainite phase or mixed phaseof martensite and austenite. The Co base hard phase includes theprecipitated material mainly composed of Mo silicide integrallyprecipitated in the Co base hard phase. The Fe base hard phase includesgranular Cr carbide, Mo carbide, V carbide, and W carbide precipitatedin the Fe base hard phase.

In the manufacturing method for the first and second wear resistantsintered alloys of the invention, preferred additive elements areexplained below.

(1) Addition of Lead, Molybdenum Disulfide, Manganese Sulfide, BoronNitride, Magnesium Metasilicate Mineral, and Calcium Fluoride Powder

To improve the machinability of the wear resistant sintered alloy of theinvention, the mixed powder may comprise at least one type selected fromthe group consisting of lead powder, molybdenum disulfide powder,manganese sulfide powder, boron nitride powder, magnesium metasilicatemineral powder, and calcium fluoride powder, by 0.3 to 2.0 mass % of themixed powder. The reasons for limiting the contents of the additives arethe same as explained earlier.

(2) Infiltration or Impregnation of Lead, Lead Alloy, Copper, CopperAlloy, and Acrylic Resin

In the pores of the wear resistant sintered alloy of the inventionmanufactured in this manufacturing method, lead, lead alloy, copper,copper alloy, and acrylic resin can be infiltrated or impregnated. Morespecifically, by adding powder of lead or copper in the mixed powder,and sintering the powder formed body, these metals are melt and filled(infiltrated) in the pores. Alternatively, by filling a closed containerwith fused acrylic resin or wear resistant sintered alloy, andevacuating the closed container, the pores may be filled with acrylicresin (impregnated). Instead of acrylic resin, by using fused lead orcopper or copper alloy, these metals can also be infiltrated in thepores.

EMBODIMENTS Embodiment 1

Effects of Composition of Alloy Powder for Forming Hard Phase

As alloy powder for forming matrix, alloy powder of Fe-6.5Co-1.5 Mo—Nidisclosed in patent reference 2 was prepared, and the alloy powder forforming the hard phase in the composition shown in Table 1 was added andmixed by 25 mass %, together with 1.1 mass % of graphite powder andforming lubricant (0.8 mass % of zinc stearate), and the mixed powderwas formed in a ring of φ30 (mm)×φ20 (mm)×h10 (mm) at forming pressureof 650 MPa. TABLE 1 Composition of alloy Wear amount powder for formingμm Sample hard phase, mass % Valve No. Co Mo Cr Si seat Valve TotalRemarks 01 Balance 45.0 10.0 3.0 150 25 175 Out of scope of invention 02Balance 48.0 10.0 3.0 110 8 118 03 Balance 50.0 10.0 3.0 85 5 90 04Balance 55.0 10.0 3.0 80 5 85 05 Balance 60.0 10.0 3.0 90 9 99 06Balance 65.0 10.0 3.0 165 38 203 Out of scope of invention 07 Balance50.0 0.0 3.0 180 0 180 Out of scope of invention 08 Balance 50.0 3.0 3.0120 1 121 09 Balance 50.0 5.0 3.0 92 3 95 10 Balance 50.0 12.0 3.0 105 5110 11 Balance 50.0 15.0 3.0 165 10 175 Out of scope of invention 12Balance 50.0 10.0 0.0 250 0 250 Out of scope of invention 13 Balance50.0 10.0 1.0 101 2 103 14 Balance 50.0 10.0 5.0 75 6 81 15 Balance 50.010.0 7.0 200 8 208 Out of scope of invention 16 Balance 28.0 8.0 2.5 14923 172 Prior art

These formed bodies were sintered at 1180° C. for 60 minutes in andecomposed ammonia gas atmosphere, and samples 01 to 16 were prepared.In these samples, simplified wear tests were conducted, and the resultsare shown in Table 1.

The simplified wear tests were conducted in the loaded state of strikingand contacting at high temperature. More specifically, the ring testpiece was processed into a valve seat shape having a slope of 45 degreesat the inner side, and the sintered alloy was press-fitted into analuminum alloy housing. On an outer surface made of SUH-36 which washeat resisting steel defined by the JIS (Japan Industrial Standards), acircular contacting member (valve) partially having a slope of 45degrees was driven by motor, and vertical piston motions were caused byrotation of an eccentric cam, and sloped sides of the sintered alloy andcontacting member were repeatedly contacted. That is, valve motions arerepeated actions of releasing motion of departing from the valve seat bythe eccentric cam rotated by motor driving, and contacting motion on thevalve seat by the valve spring, and vertical piston motions arerealized. In this test, the contacting member was heated by a burner andthe temperature was set to the sintered alloy temperature of 300° C.,and strike operations in the simplified wear test were 2800times/minute, and the duration was 15 hours. In this manner, the wear ofthe valve seats and the wear of valves after the tests were measured andevaluated.

Referring now to FIG. 5 to FIG. 7, test results are discussed. Dottedlines in FIG. 5 to FIG. 7 show the wear level (total wear of valve seatand valve) of sample 16 (prior art).

(Relationship between Wear and Mo Amount in Alloy Powder for FormingHard Phase)

As shown in FIG. 5, in sintered alloys (samples 02 to 05) in which Mocontent in alloy powder for forming the hard phase is in a range of 48to 60 mass %, the wear amount of valve seat and valve is stable and low,and a favorable wear resistance is exhibited. On the other hand, insintered alloys (samples 01 and 06) in which the Mo content is out ofthe range of 48 to 60 mass %, in particular, the wear amount of valveseat is significantly high, and the wear amount of valve is alsorelatively high. It has been therefore confirmed that an excellent wearresistance is realized as long as the Mo content in alloy powder forforming hard phase is in a range of 48 to 60 mass %.

(Relationship between Wear and Cr Amount in Alloy Powder for FormingHard Phase)

As shown in FIG. 6, in sintered alloys (samples 03 and 08 to 10) inwhich the Cr content in the alloy powder for forming the hard phase isin a range of 3 to 12 mass %, the wear amount of the valve seat andvalve is stable and low, and a favorable wear resistance is exhibited.On the other hand, in sintered alloys (samples 07 and 11) in which theCr content is out of the range of 3 to 12 mass %, in particular, thewear amount of the valve seat is significantly high. It has beentherefore confirmed that an excellent wear resistance is realized aslong as the Cr content in the alloy powder for forming the hard phase isin a range of 3 to 12 mass %.

(Relationship between Wear and Si Amount in Alloy Powder for FormingHard Phase)

As shown in FIG. 7, in sintered alloys (samples 03, 13 and 14) in whichthe Si content in the alloy powder for forming the hard phase is in arange of 1 to 5 mass %, the wear amount of the valve seat and the valveis stable and low, and a favorable wear resistance is exhibited. On theother hand, in sintered alloys (samples 12 and 15) in which the Sicontent is out of the range of 1 to 5 mass %, in particular, the wearamount of the valve seat is significantly high. It has been thereforeconfirmed that an excellent wear resistance is realized as long as theSi content in the alloy powder for forming hard phase is in a range of 1to 5 mass %.

Embodiment 2

Effects of Content of Alloy Powder for Forming Hard Phase

As the alloy powder for forming matrix, an alloy powder ofFe-6.5Co-1.5Mo—Ni disclosed in patent reference 2 was prepared, and thealloy powder for forming hard phase used in sample 03 in embodiment 1was used, and the alloy powder for forming hard phase added by theamount as shown in Table 2, and a ring of φ30 (mm)×φ20 (mm)×h10 wasformed under the same condition as in embodiment 1. TABLE 2 Content ofalloy Sample powder for forming Wear amount, μm No. hard phase, mass %Valve seat Valve Total Remarks 17 0.0 263 0 263 Out of scope ofinvention 18 5.0 158 1 159 19 15.0 110 2 112 20 20.0 95 3 98 03 25.0 855 90 21 30.0 90 7 97 22 40.0 108 17 125 23 50.0 150 53 203 Out of scopeof invention 16 25.0 149 23 172 Prior art

These formed bodies were sintered at 1180° C. for 60 minutes indecomposed ammonia gas atmosphere, and samples 17 to 23 were prepared.In these samples, simplified wear tests were conducted, and results arein Table 2 with the results of sample 03 and 16 in embodiment 1.

Referring now to FIG. 8, test results are discussed. Dotted lines inFIG. 8 show the wear level (total wear of valve seat and valve) ofsample 16 (prior art).

(Relationship between Wear and Content of Alloy Powder for Forming HardPhase)

As shown in FIG. 8, in sintered alloys (samples 03 and 18 to 22) inwhich content of the alloy powder for forming the hard phase in theoverall mass of mixed powder is in a range of 5 to 40 mass %, the wearamount of the valve seat and valve is stable and low, and a favorablewear resistance is exhibited. On the other hand, in sintered alloys(samples 17 and 23) in which content of alloy powder for forming hardphase is out of the range of 5 to 40 mass %, in particular, the wearamount of valve seat is significantly high. It has been thereforeconfirmed that an excellent wear resistance is realized as long as thecontent of alloy powder for forming the hard phase in the overall massof mixed powder is in a range of 5 to 40 mass %.

Embodiment 3

Effects of Sintering Temperature

As the alloy powder for forming the matrix, an alloy powder ofFe-6.5Co-1.5Mo—Ni disclosed in patent reference 2 was prepared, and thealloy powder for forming the hard phase used in sample 03 in embodiment1 was used, and the sintering temperature was set as shown in Table 3,and a ring of φ30 (mm)×φ20 (mm)×h10 (mm) was formed under the samecondition as in embodiment 1. TABLE 3 Sample Sintering Wear amount, μmNo. temperature ° C. Valve seat Valve Total Remarks 24 900 300 0 300 Outof scope of invention 25 1000 130 2 132 26 1100 100 4 104 03 1180 85 590 27 1200 80 6 86 28 1230 210 3 213 Out of scope of invention 16 1180149 23 172 Prior art

These formed bodies were sintered for 60 minutes in an decomposedammonia gas atmosphere, and samples 24 to 28 were prepared. In thesesamples, simplified wear tests were conducted, and the results are shownin Table 3 with the results of sample 03 and 16 in embodiment 1.

Referring now to FIG. 9, test results are discussed. Dotted lines inFIG. 9 show the wear level (total wear of valve seat and valve) ofsample 16 (prior art).

(Relationship between Wear and Sintering Temperature)

As shown in FIG. 9, in sintered alloys (samples 03 and 25 to 27) inwhich the sintering temperature is in a range of 1000 to 1200° C., thewear amount of the valve seat and the valve is stable and low, and afavorable wear resistance is exhibited. On the other hand, in sinteredalloys (samples 24 and 28) in which the sintering temperature is out ofthe range of 1000 to 1200° C., in particular, the wear amount of thevalve seat is significantly high. It has been therefore confirmed thatan excellent wear resistance is realized as long as the sinteringtemperature is in a range of 1000 to 1200° C.

Embodiment 4

Effects of Hard Phase

As the alloy powder for forming matrix, an alloy powder ofFe-3Cr-0.3Mo-0.3V disclosed in patent reference 1, and alloy powder ofFe-6.5Co-1.5Mo—Ni were prepared independently, or these alloy powderswere mixed at a rate of 1:1, and a mixed powder was prepared. Further,as the alloy powder for forming the hard phase, Co-50Mo-10Cr-3Si alloyof the invention, and conventional Fe-3Cr-0.3Mo-0.3V alloy wereprepared. By adding 25 mass % of alloy powder for forming the hard phaseand 1.1 mass % of graphite powder were added to the powder for formingmatrix in the composition shown in Table 4, and a ring of φ30 (mm)×φ20(mm)×h10 (mm) was formed under the same condition as in embodiment 1.TABLE 4 Alloy powder for Ratio of powder for Wear amount, μm Sampleforming hard forming matrix Valve No phase Fe—6.5Co—1.5Mo—1.5NiFe—3Cr—0.3Mo-0.3v seat Valve Total Remarks 03 Co—50Mo—10Cr—3Si 100 85 590 29 Co—50Mo—10Cr—3Si 100 120 5 125 30 Co—50Mo—10Cr—3Si 50 50 108 5 11316 Co—28Mo—8Cr—2.5Si 100 149 23 172 Prior art 31 Co—28Mo—8Cr—2.5Si 100183 25 208 Prior art 32 Co—28Mo—8Cr—2.5Si 50 50 174 25 199 Prior art

These formed bodies were sintered at 1180° C. for 60 minutes in andecomposed ammonia gas atmosphere, and samples 29 to 32 were prepared.In these samples, simplified wear tests were conducted, and results areshown in Table 4 with the results of sample 03 and 16 in embodiment 1.

Referring now to FIG. 10, test results are discussed.

(Relationship between Wear and Hard Phase)

As shown in FIG. 10, when the alloy powder for forming the hard phase ofthe invention is used (samples 03, 29 and 30), regardless of the type ofalloy powder for forming the matrix, the wear amount of the valve seatand the valve is stable and low, as compared with the case of using theconventional alloy powder for forming the hard phase (samples 16, 31 and32), and a favorable wear resistance is exhibited. It has been thereforeconfirmed that an excellent wear resistance is realized by using thealloy powder for forming the hard phase of the invention.

Embodiment 5

Effects of Composition and Content of Alloy Powder for Forming Co BaseHard Phase (Alloy Powder B)

Alloy powder A for forming the matrix, alloy powder B for forming the Cobase hard phase, alloy powder C for forming the Fe base hard phase, andgraphite powder shown in Table 5 were blended at the rate specified inTable 5, together with forming lubricant (0.8 mass % of zinc stearate),and the mixed powder was formed in a ring of φ30 (mm)×φ20 (mm)×h10 (mm)at a forming pressure of 650 MPa. TABLE 5 Blending ratio, mass % AlloyAlloy powder B Sintering Sample powder A Composition, mass % Alloypowder C Graphite temperature No. Fe—5Mo Co Mo Si Cr Fe—5Mo—2V—6W—4Cr—1Cpowder ° C. 41 Balance 25.00 Balance 45.00 3.00 10.00 20.00 0.70 1180 42Balance 25.00 Balance 48.00 3.00 10.00 20.00 0.70 1180 43 Balance 25.00Balance 50.00 3.00 10.00 20.00 0.70 1180 44 Balance 25.00 Balance 55.003.00 10.00 20.00 0.70 1180 45 Balance 25.00 Balance 60.00 3.00 10.0020.00 0.70 1180 46 Balance 25.00 Balance 65.00 3.00 10.00 20.00 0.701180 47 Balance 25.00 Balance 50.00 0.50 10.00 20.00 0.70 1180 48Balance 25.00 Balance 50.00 1.00 10.00 20.00 0.70 1180 49 Balance 25.00Balance 50.00 5.00 10.00 20.00 0.70 1180 50 Balance 25.00 Balance 50.007.00 10.00 20.00 0.70 1180 51 Balance 25.00 Balance 50.00 3.00 — 20.000.70 1180 52 Balance 25.00 Balance 50.00 3.00  3.00 20.00 0.70 1180 53Balance 25.00 Balance 50.00 3.00  5.00 20.00 0.70 1180 54 Balance 25.00Balance 50.00 3.00 12.00 20.00 0.70 1180 55 Balance 25.00 Balance 50.003.00 15.00 20.00 0.70 1180 56 Balance — Balance 50.00 3.00 10.00 20.000.70 1180 57 Balance  5.00 Balance 50.00 3.00 10.00 20.00 0.70 1180 58Balance 15.00 Balance 50.00 3.00 10.00 20.00 0.70 1180 59 Balance 40.00Balance 50.00 3.00 10.00 20.00 0.70 1180 60 Balance 50.00 Balance 50.003.00 10.00 20.00 0.70 1180

These formed bodies were sintered at 1180° C. for 60 minutes in andecomposed ammonia gas atmosphere, and samples 41 to 60 were prepared.In these samples, simplified wear tests were conducted, and results areshown in Table 6. TABLE 6 Wear amount, μm Sample Overall composition,mass % Valve No. Fe Mo Co Si Cr V W C seat Valve Total 41 Balance 14.9710.50 0.75 3.30 0.40 1.20 0.90 100 19 119 42 Balance 15.72 9.75 0.753.30 0.40 1.20 0.90 68 5 73 43 Balance 16.22 9.25 0.75 3.30 0.40 1.200.90 55 3 58 44 Balance 17.47 8.00 0.75 3.30 0.40 1.20 0.90 51 3 54 45Balance 18.72 6.75 0.75 3.30 0.40 1.20 0.90 60 5 65 46 Balance 19.975.50 0.75 3.30 0.40 1.20 0.90 130 28 158 47 Balance 16.22 9.88 0.13 3.300.40 1.20 0.90 200 0 200 48 Balance 16.22 9.75 0.25 3.30 0.40 1.20 0.9086 0 86 49 Balance 16.22 8.75 1.25 3.30 0.40 1.20 0.90 50 3 53 50Balance 16.22 8.25 1.75 3.30 0.40 1.20 0.90 150 5 155 51 Balance 16.2211.75 0.75 0.80 0.40 1.20 0.90 150 0 150 52 Balance 16.22 11.00 0.751.55 0.40 1.20 0.90 95 1 96 53 Balance 16.22 10.50 0.75 2.05 0.40 1.200.90 60 3 63 54 Balance 16.22 8.75 0.75 3.80 0.40 1.20 0.90 75 3 78 55Balance 16.22 8.00 0.75 4.55 0.40 1.20 0.90 150 5 155 56 Balance 4.97 —— 0.80 0.40 1.20 0.90 320 0 320 57 Balance 7.22 1.85 0.15 1.30 0.40 1.200.90 86 2 88 58 Balance 11.72 5.55 0.45 2.30 0.40 1.20 0.90 74 2 76 59Balance 22.97 14.80 1.20 4.80 0.40 1.20 0.90 78 8 86 60 Balance 27.4718.50 1.50 5.80 0.40 1.20 0.90 120 52 172

The simplified wear tests were conducted in the loaded state of strikingand sliding at high temperature. More specifically, the ring test piecewas processed into a valve seat shape having a slope of 45 degrees atthe inner side, and the sintered alloy was press-fitted into an aluminumalloy housing. On an outer surface made of SUH-36 material, a circularcontacting member (valve) having a slope of 45 degrees in part wasdriven by motor, and vertical piston motions were caused by rotation ofeccentric cam, and slope sides of the sintered alloy and contactingmember were repeatedly contacted. That is, valve motions are repeatedactions of releasing motion of departing from the valve seat by theeccentric cam rotated by motor driving, and contacting motion on thevalve seat by the valve spring, and vertical piston motions arerealized. In this test, the contacting member was heated by a burner andthe temperature was set to the sintered alloy temperature of 300° C.,and striking operations of simplified wear test were 2800 times/minute,and the duration of repetition was 15 hours. In this manner, the wear ofthe valve seats and wear of the valves after testing were measured andevaluated.

Referring now to FIG. 11 to FIG. 14, test results are discussed.

(Relationship between Wear and Mo Amount in Alloy Powder B)

As shown in FIG. 11, in sintered alloys (samples 42 to 45) in which Mocontent in alloy B is in a range of 48 to 60 mass %, the wear amounts ofthe valve seats and the valves are stable and low, and a favorable wearresistance is exhibited. On the other hand, in sintered alloys (samples41 and 46) in which the Mo content is out of the range of 48 to 60 mass%, in particular, the wear amount of the valve seat is significantlyhigh, and the wear amount of valve is also high relatively. It has beentherefore confirmed that an excellent wear resistance is realized aslong as the Mo content in the alloy powder B is in a range of 48 to 60mass %.

(Relationship between Wear and Si Amount in Alloy Powder B)

As shown in FIG. 12, in sintered alloys (samples 43, 48 and 49) in whichthe Si content in the alloy powder B is in a range of 1 to 5 mass %, thewear amounts of the valve seats and the valves are stable and low, and afavorable wear resistance is exhibited. On the other hand, in sinteredalloys (samples 47and 50) in which the Si content is out of the range of1 to 5 mass %, in particular, the wear amount of the valve seat issignificantly high. It has been therefore confirmed that an excellentwear resistance is realized as long as the Si content in alloy powder Bis in a range of 1 to 5 mass %.

(Relationship between Wear and Cr Amount in Alloy Powder B)

As shown in FIG. 13, in sintered alloys (samples 43 and 52 to 54) inwhich the Cr content in the alloy powder B is in a range of 3 to 12 mass%, the wear amounts of the valve seat and the valves are stable and low,and a favorable wear resistance is exhibited. On the other hand, insintered alloys (samples 51 and 55) in which the Cr content is out ofthe range of 3 to 12 mass %, in particular, the wear amounts of valveseats are significantly high. It has been therefore confirmed that anexcellent wear resistance is realized as long as the Cr content in thealloy powder B is in a range of 3 to 12 mass %.

(Relationship between Wear and Content of Alloy Powder B)

As shown in FIG. 14, in sintered alloys (samples 43 and 57 to 59) inwhich the content of alloy powder B in the overall mass of mixed powderis in a range of 5 to 40 mass %, the wear amounts of the valve seats andvalves are stable and low, and a favorable wear resistance is exhibited.On the other hand, in sintered alloys (samples 56 and 60) in which thecontent of the alloy powder B is out of the range of 5 to 40 mass %, inparticular, the wear amounts of the valve seats are significantly high.It has been therefore confirmed that an excellent wear resistance isrealized as long as the content of alloy powder B in the overall mass ofmixed powder is in a range of 5 to 40 mass %.

Embodiment 6

Effects of Composition and Content of Alloy Powder for Forming Matrix(Alloy Powder A)

Alloy powder A for forming the matrix, alloy powder B for forming the Cobase hard phase, alloy powder C for forming the Fe base hard phase, andgraphite powder shown in Table 7 were blended at the rates specified inTable 7, together with forming lubricant (0.8 mass % of zinc stearate),and the mixed powder was formed in a ring of φ30 (mm)×φ20 (mm)×h10 (mm)at forming pressure of 650 MPa. These formed bodies were sintered underthe same condition as in embodiment 5, and samples 43 and 61 to 64 inthe composition as shown in Table 8 were prepared. In samples,simplified wear tests were conducted as in embodiment 5, e results areshown in Table 8. TABLE 7 Blending ratio, mass % Alloy powder AComposition, Sintering Sample mass % Alloy powder B Alloy powder CGraphite temperature No. Fe Mo Co—50Mo—3Si—10Cr Fe—5Mo—2V—6W—4Cr—1Cpowder ° C. 61 Balance Balance — 25.00 20.00 0.70 1180 62 BalanceBalance 3.00 25.00 20.00 0.70 1180 43 Balance Balance 5.00 25.00 20.000.70 1180 63 Balance Balance 7.00 25.00 20.00 0.70 1180 64 BalanceBalance 10.00 25.00 20.00 0.70 1180

TABLE 8 Wear amount, μm Sample Overall composition, mass % Valve No. FeMo Co Si Cr V W C seat Valve Total 61 Balance 13.50 9.25 0.75 3.30 0.401.20 0.90 180 0 180 62 Balance 15.13 9.25 0.75 3.30 0.40 1.20 0.90 78 280 43 Balance 16.22 9.25 0.75 3.30 0.40 1.20 0.90 55 3 58 63 Balance17.30 9.25 0.75 3.30 0.40 1.20 0.90 60 5 65 64 Balance 18.93 9.25 0.753.30 0.40 1.20 0.90 150 4 154

Referring now to FIG. 15, test results are discussed.

(Relationship between Wear and Mo Amount in Alloy Powder A)

As shown in FIG. 15, in sintered alloys (samples 43, 62 and 63) in whichthe Mo content in alloy powder A is in a range of 3 to 7 mass %, thewear amounts of valve seats and valves are stable and low, and afavorable wear resistance is exhibited. On the other hand, in sinteredalloys (samples 61 and 64) in which the Mo content is out of the rangeof 3 to 7 mass %, in particular, the wear amounts of the valve seats aresignificantly high. It has been therefore confirmed that an excellentwear resistance is realized as long as the Mo content in alloy powder Ais in a range of 3 to 7 mass %.

Embodiment 7

Effects of Composition and Content of Alloy Powder for Forming Fe BaseHard Phase (Alloy Powder C)

Alloy powder A for forming the matrix, alloy powder B for forming the Cobase hard phase, alloy powder C for forming the Fe base hard phase, andgraphite powder shown in Table 9 were blended at the rates specified inTable 7, together with forming lubricant (0.8 mass % of zinc stearate),and the mixed powder was formed in a ring of φ30 (mm)×φ20 (mm)×h10 (mm)at a forming pressure of 650 MPa. These formed bodies were sinteredunder the same conditions as in embodiment 5, and samples 03 and 25 to43 in the composition as shown in Table 10 were prepared. In thesesamples, simplified wear tests were conducted as in embodiment 5, andthe results are shown in Table 10. TABLE 9 Blending ratio, mass % AlloyAlloy powder C Sintering Sample powder A Alloy powder B Composition,mass % Graphite temperature No. Fe—5Mo Co—50Mo—3Si—10Cr Fe Mo V W Cr Cpowder ° C. 65 Balance 25.00 20.00 Balance 2.00 6.00 4.00 1.00 0.70 118066 Balance 25.00 20.00 Balance 4.00 5.00 6.00 4.00 1.00 0.70 1180 43Balance 25.00 20.00 Balance 5.00 2.00 6.00 4.00 1.00 0.70 1180 67Balance 25.00 20.00 Balance 8.00 5.00 6.00 4.00 1.00 0.70 1180 68Balance 25.00 20.00 Balance 10.00 2.00 6.00 4.00 1.00 0.70 1180 69Balance 25.00 20.00 Balance 5.00 — — — 1.00 0.70 1180 70 Balance 25.0020.00 Balance 5.00 0.50 4.00 2.00 1.00 0.70 1180 71 Balance 25.00 20.00Balance 5.00 3.00 8.00 6.00 1.00 0.70 1180 72 Balance 25.00 20.00Balance 5.00 4.00 10.00 7.00 1.00 0.70 1180 73 Balance 25.00 20.00Balance 5.00 2.00 6.00 4.00 0.40 0.70 1180 74 Balance 25.00 20.00Balance 5.00 2.00 6.00 4.00 0.60 0.70 1180 75 Balance 25.00 20.00Balance 5.00 2.00 6.00 4.00 1.20 0.70 1180 76 Balance 25.00 20.00Balance 5.00 2.00 6.00 4.00 1.60 0.70 1180 77 Balance 25.00 — Balance5.00 2.00 6.00 4.00 1.00 0.70 1180 78 Balance 25.00  5.00 Balance 5.002.00 6.00 4.00 1.00 0.70 1180 79 Balance 25.00 10.00 Balance 5.00 2.006.00 4.00 1.00 0.70 1180 80 Balance 25.00 15.00 Balance 5.00 2.00 6.004.00 1.00 0.70 1180 81 Balance 25.00 25.00 Balance 5.00 2.00 6.00 4.001.00 0.70 1180 82 Balance 25.00 30.00 Balance 5.00 2.00 6.00 4.00 1.000.70 1180 83 Balance 25.00 35.00 Balance 5.00 2.00 6.00 4.00 1.00 0.701180

TABLE 10 Wear amount, μm Sample Overall composition, mass % Valve No. FeMo Co Si Cr V W C seat Valve Total 65 Balance 15.22 9.25 0.75 3.30 0.401.20 0.90 150 2 152 66 Balance 16.02 9.25 0.75 3.30 1.00 1.20 0.90 65 368 43 Balance 16.22 9.25 0.75 3.30 0.40 1.20 0.90 55 3 58 67 Balance16.82 9.25 0.75 3.30 1.00 1.20 0.90 60 3 63 68 Balance 17.22 9.25 0.753.30 0.40 1.20 0.90 80 50 130 69 Balance 16.22 9.25 0.75 2.50 — — 0.90160 2 162 70 Balance 16.22 9.25 0.75 2.90 0.10 0.80 0.90 76 3 79 71Balance 16.22 9.25 0.75 3.70 0.60 1.60 0.90 62 18 80 72 Balance 16.229.25 0.75 3.90 0.80 2.00 0.90 115 60 175 73 Balance 16.22 9.25 0.75 3.300.40 1.20 0.78 130 2 132 74 Balance 16.22 9.25 0.75 3.30 0.40 1.20 0.8276 2 78 75 Balance 16.22 9.25 0.75 3.30 0.40 1.20 0.94 60 10 70 76Balance 16.22 9.25 0.75 3.30 0.40 1.20 1.02 105 38 143 77 Balance 16.229.25 0.75 2.50 — — 0.70 160 2 162 78 Balance 16.22 9.25 0.75 2.70 0.100.30 0.75 94 2 96 79 Balance 16.22 9.25 0.75 2.90 0.20 0.60 0.80 80 3 8380 Balance 16.22 9.25 0.75 3.10 0.30 0.90 0.85 62 3 65 81 Balance 16.229.25 0.75 3.50 0.50 1.50 0.95 54 4 58 82 Balance 16.22 9.25 0.75 3.700.60 1.80 1.00 60 16 76 83 Balance 16.22 9.25 0.75 3.90 0.70 2.10 1.05110 54 164

Referring now to FIG. 16 to FIG. 19, test results are discussed.

(Relationship between Wear and Mo Amount in Alloy Powder C)

As shown in FIG. 16, in sintered alloys (samples 43, 66 and 67) in whichthe Mo content in the alloy C is in a range of 4 to 8 mass %, the wearamounts of the valve seat and the valves are stable and low, and afavorable wear resistance is exhibited. On the other hand, in sinteredalloys (samples 65 and 68) in which the Mo content is out of the rangeof 4 to 8 mass %, in particular, the wear amount of the valve seats issignificantly high. It has been therefore confirmed that an excellentwear resistance is realized as long as the Mo content in alloy powder Cis in a range of 4 to 8 mass %.

(Relationship between Wear and Amount of Alloying Elements (V, W, Cr) inalloy powder C)

As shown in FIG. 17, in sintered alloys (samples 43, 70 and 71) in whichthe content of alloying elements in alloy powder C is in a range of V:0.5 to 3 mass %, W: 4 to 8 mass %, and Cr: 2 to 6 mass %, the wearamounts of the valve seats and the valves are stable and low, andfavorable wear resistance was exhibited. On the other hand, in sinteredalloys (samples 69 and 72) in which the content of alloying elements inalloy powder C is out of the range of V: 0.5 to 3 mass %, W: 4 to 8 mass%, and Cr: 2 to 6 mass %, in particular, the wear amounts of valve seatswas significantly high. It has been therefore confirmed that anexcellent wear resistance is realized as long as the content of alloyingelements in alloy powder C is in a range of V: 0.5 to 3 mass %, W: 4 to8 mass %, and Cr: 2 to 6 mass %.

(Relationship between Wear and C Amount in Alloy Powder C)

As shown in FIG. 18, in sintered alloys (samples 43, 74 and 75) in whichthe C content in the alloy powder C is in a range of 0.6 to 1.2 mass %,the wear amounts of the valve seats and the valves were stable and low,and favorable wear resistance was exhibited. On the other hand, insintered alloys (samples 73 and 76) in which the C content is out of therange of 0.6 to 1.2 mass %, in particular, the wear amounts of valveseats are significantly high. It has been therefore confirmed that anexcellent wear resistance is realized as long as the C content in alloypowder C is in a range of 0.6 to 1.2 mass %.

(Relationship between Wear and Content of Alloy Powder C)

As shown in FIG. 19, in sintered alloys (samples 43 and 78 to 82) inwhich the content of alloy powder C in the overall mass of mixed powderis in a range of 5 to 30 mass %, the wear amounts of the valve seats andthe valves were stable and low, and favorable wear resistance wasexhibited. On the other hand, in sintered alloys (samples 77 and 83) inwhich the content of the alloy powder C is out of the range of 5 to 30mass %, in particular, the wear amounts of valve seats weresignificantly high. It has been therefore confirmed that an excellentwear resistance is realized as long as the content of alloy powder C inthe overall mass of mixed powder is in a range of 5 to 30 mass %.

Embodiment 8

Effects of Addition of Ni Powder

Alloy powder A for forming the matrix, alloy powder B for forming the Cobase hard phase, alloy powder C for forming the Fe base hard phase, Nipowder, and graphite powder shown in Table 11 were blended at the ratespecified in Table 11, together with forming lubricant (0.8 mass % ofzinc stearate), and the mixed powder was formed in a ring of φ30(mm)×φ20 (mm)×h10 (mm) at a forming pressure of 650 MPa. These formedbodies were sintered under the same condition as in embodiment 5, andsamples 43 and 84 to 88 in the compositions as shown in Table 12 wereprepared. In these samples, simplified wear tests were conducted as inembodiment 5, and the results are shown in Table 12. TABLE 11 Blendingratio, mass % Alloy Sintering Sample powder A Alloy powder B Alloypowder C Ni Graphite temperature No. Fe—5Mo Fe—50Mo—3Si—10CrFe—5Mo—2V—6W—4Cr—1C powder powder ° C. 43 Balance 25.00 20.00 — 0.701180 84 Balance 25.00 20.00 3.00 0.70 1180 85 Balance 25.00 20.00 5.000.70 1180 86 Balance 25.00 20.00 10.00 0.70 1180 87 Balance 25.00 20.0013.00 0.70 1180 88 Balance 25.00 20.00 15.00 0.70 1180

TABLE 12 Wear amount, μm Sample Overall composition, mass % Valve No. FeMo Co Si Cr V W C Ni seat Valve Total 43 Balance 16.22 9.25 0.75 3.300.40 1.20 0.90 — 55 3 58 84 Balance 16.07 9.25 0.75 3.30 0.40 1.20 0.903.00 36 6 42 85 Balance 15.97 9.25 0.75 3.30 0.40 1.20 0.90 5.00 31 7 3886 Balance 15.72 9.25 0.75 3.30 0.40 1.20 0.90 10.00 28 12 40 87 Balance15.57 9.25 0.75 3.30 0.40 1.20 0.90 13.00 40 9 49 88 Balance 15.47 9.250.75 3.30 0.40 1.20 0.90 15.00 105 6 111

Referring now to FIG. 20, test results are discussed.

(Relationship between Wear and Content of Ni Powder)

As shown in FIG. 20, in sintered alloys (samples 43 and 84 to 87) inwhich the content of the Ni powder is in a range of 13 mass % or less,the wear amounts of the valve seats and valves are stable and low, andfavorable wear resistance was exhibited. On the other hand, in sinteredalloy (sample 88) in which the content of the Ni powder is out of therange of 13 mass % or less, and in particular, the wear amounts of thevalve seats were significantly high. It has been therefore confirmedthat excellent wear resistance is realized as long as the content of theNi powder is in a range of 13 mass % or less.

Embodiment 9

Effects of Addition of Graphite Powder

Alloy powder A for forming the matrix, alloy powder B for forming the Cobase hard phase, alloy powder C for forming the Fe base hard phase, andgraphite powder shown in Table 13 were blended at the rates specified inTable 13, together with forming lubricant (0.8 mass % of zinc stearate),and the mixed powder was formed in a ring of φ30 (mm)×φ20 (mm)×h10 (mm)at a forming pressure of 650 MPa. These formed bodies were sinteredunder the same condition as in embodiment 5, and samples 43 and 89 to 94in the composition as shown in Table 14 were prepared. In these samples,simplified wear tests were conducted as in embodiment 5, and the resultsare shown in Table 14. TABLE 13 Blending ratio, mass % Alloy SinteringSample powder A Alloy powder B Alloy powder C Graphite temperature No.Fe—5Mo Fe—50Mo—3Si—10Cr Fe—5Mo—2V—6W—4Cr—1C powder ° C. 89 Balance 25.0020.00 0.10 1180 90 Balance 25.00 20.00 0.30 1180 91 Balance 25.00 20.000.50 1180 43 Balance 25.00 20.00 0.70 1180 92 Balance 25.00 20.00 1.001180 93 Balance 25.00 20.00 1.20 1180 94 Balance 25.00 20.00 1.50 1180

TABLE 14 Wear amount, μm Sample Overall composition, mass % Valve No. FeMo Co Si Cr V W C seat Valve Total 89 Balance 16.25 9.25 0.75 3.30 0.401.20 0.30 180 0 180 90 Balance 16.24 9.25 0.75 3.30 0.40 1.20 0.50 80 282 91 Balance 16.23 9.25 0.75 3.30 0.40 1.20 0.70 60 3 63 43 Balance16.22 9.25 0.75 3.30 0.40 1.20 0.90 55 3 58 92 Balance 16.20 9.25 0.753.30 0.40 1.20 1.20 52 3 55 93 Balance 16.19 9.25 0.75 3.30 0.40 1.201.40 63 8 71 94 Balance 16.19 9.25 0.75 3.30 0.40 1.20 1.70 103 33 136

Referring now to FIG. 21, test results are discussed.

(Relationship between Wear and Content of Graphite Powder)

As shown in FIG. 21, in sintered alloys (samples 43 and 90 to 93) inwhich content of graphite powder is in a range of 0.3 to 1.2 mass %, thewear amounts of the valve seats and valves were stable and low, andfavorable wear resistance was exhibited. On the other hand, in sinteredalloys (samples 89 and 94) in which the content of graphite powder isout of the range of 0.3 to 1.2 mass %, in particular, the wear amountsof the valve seats were significantly high. It has been thereforeconfirmed that excellent wear resistance is realized as long as thecontent of graphite powder is in a range of 0.3 to 1.2 mass %.

Embodiment 10

Effects of Sintering Temperature

Alloy powder A for forming the matrix, alloy powder B for forming the Cobase hard phase, alloy powder C for forming the Fe base hard phase, andgraphite powder shown in Table 15 were blended at the rates specified inTable 15, together with forming lubricant (0.8 mass % of zinc stearate),and the mixed powder was formed in a ring of φ30 (mm)×φ20 (mm)×h10 (mm)at a forming pressure of 650 MPa. These formed bodies were sinteredunder the same conditions as in embodiment 5, and samples 43 and 95 to99 in the composition as shown in Table 16 were prepared. In thesesamples, simplified wear tests were conducted as in embodiment 5, andthe results are shown in Table 16. TABLE 15 Blending ratio, mass % AlloySintering Sample powder A Alloy powder B Alloy powder C Graphitetemperature No. Fe—5Mo Fe—50Mo—3Si—10Cr Fe—5Mo—2V—6W—4Cr—1C powder ° C.95 Balance 25.00 20.00 0.70 900 96 Balance 25.00 20.00 0.70 1000 97Balance 25.00 20.00 0.70 1100 43 Balance 25.00 20.00 0.70 1180 98Balance 25.00 20.00 0.70 1200 99 Balance 25.00 20.00 0.70 1230

TABLE 16 Wear amount, μm Sample Overall composition, mass % Valve No. FeMo Co Si Cr V W C seat Valve Total 95 Balance 16.22 9.25 0.75 3.30 0.401.20 0.90 280 0 280 96 Balance 16.22 9.25 0.75 3.30 0.40 1.20 0.90 85 287 97 Balance 16.22 9.25 0.75 3.30 0.40 1.20 0.90 65 2 67 43 Balance16.22 9.25 0.75 3.30 0.40 1.20 0.90 55 3 58 98 Balance 16.22 9.25 0.753.30 0.40 1.20 0.90 50 3 53 99 Balance 16.22 9.25 0.75 3.30 0.40 1.200.90 184 3 187

Referring now to FIG. 22, test results are discussed.

(Relationship Between Wear and Sintering Temperature)

As shown in FIG. 22, in sintered alloys (samples 43 and 96 to 98) inwhich sintering temperature is in a range of 1000 to 1200° C., the wearamounts of the valve seats and valves were stable and low, and favorablewear resistance was exhibited. On the other hand, in sintered alloys(samples 95 and 99) in which the sintering temperature was out of therange of 1000 to 1200° C., in particular, the wear amounts of valveseats were significantly high. It has been therefore confirmed that anexcellent wear resistance is realized as long as the sinteringtemperature is in a range of 1000 to 1200° C.

1. An alloy powder for forming a hard phase, consisting of Mo: 48 to 60mass %, Cr: 3 to 12 mass % and Si: 1 to 5 mass %, and the balance of Coand inevitable impurities.
 2. A ferriferous mixed powder for a wearresistant sintered alloy, wherein 5 to 40 mass % of the alloy powder forforming hard phase according to claim 1 is added to an iron base alloypowder for forming iron alloy matrix.